UP TO 150 Islamic radicals have travelled from Britain to Iraq to join up with a “British brigade” that has been established by Al-Qaeda leaders to fight coalition forces.

Senior security sources say leaders of the Iraqi insurgency have set up a “foreign legion” composed entirely of westerners to fight alongside the insurgents in the war against British and American forces. Some are preparing to carry out suicide attacks while others have received basic combat training for attacks on western troops The so-called “British brigade” is said to be operating under the direct command of Abu Musab al-Zarqawi, the leader of Al-Qaeda in Iraq. Members of the unit are thought to be in the Sunni triangle, a combat zone and Al-Qaeda hotbed west of Baghdad.

The flow of young Muslim men from western Europe to Iraq has increased dramatically in the past two years. The “pipeline” of suspected terrorists is being fuelled by growing resentment about American and British policy and scandals such as the mistreatment of inmates at the Abu Ghraib prison.

A senior security source, confirming that between 120 and 150 Britons had travelled to Iraq, said there was concern that the flow was increasing: “The really worrying thing is that this has become a movement that people believe in. It’s not simply a matter of them joining a terrorist organisation.”

The latest demonstration of the trend came 10 days ago when anti-terrorist police arrested eight men in a series of raids in Manchester, London and Merseyside.

Police said publicly that the men were being held on suspicion of encouraging and financing Al-Qaeda’s terrorist operations abroad. But privately Whitehall officials said they believed that there may have been links to the training and recruitment of volunteers for suicide missions in Iraq.

Earlier this year Charles Clarke, the former home secretary, imposed a control order on an unnamed terror suspect who had been prevented from boarding a plane at Manchester airport. Security sources say dozens of cases have been unearthed in recent months where suspected would-be suicide bombers have been stopped at British airports while they were en route to join the insurgency.

One said: “Greater Manchester police frequently interdict individuals whom they believe are going to Iraq and other locations in order to carry out suicide attacks. Conventional charges, such as passport irregularities, are used to prevent them leaving the country. But this leaves police with the problem of returning potential suicide bombers to the Manchester community.” Zarqawi has boasted on his website about the British recruits who have joined his “foreign legion”. One Zarqawi video, with English subtitles, issued last month, shows scenes of excited young recruits in Iraq. The message is “They are fighting; you should be too”.

The International Institute for Strategic Studies estimates that one in 10 of the 20,000 insurgents in Iraq was foreign-born.

However, Christopher Langton, editor of the institute’s study The Military Balance 2006, said he did not know how many of the estimated 2,000 foreigners were British.

Last month Pierre de Bousquet de Florian, head of the DST, the French domestic security service, said that about 15 young French people remained in and around Iraq. At least nine had been killed.

Muriel Degauque, 38, a white Belgian convert to Islam, blew herself up in an attack on an Iraqi police patrol in the town of Baquba, north of Baghdad, last November.

Wail al-Dhaleai, a Yemeni asylum seeker living in Sheffield, died when he drove a car filled with explosives into a US army patrol in November 2003.

The extent of the problem in this country began to emerge only last year when Idris Bazis, 41, a French-Algerian who lived in Manchester, blew himself up in a suicide attack on American troops.

An investigation by Greater Manchester police soon uncovered an extensive network for would-be “holy warriors” in Britain. A senior police source said that some went to Pakistan while others went to Middle Eastern countries, such as Syria, before being smuggled over the border.

The Ministry of Defence said it was aware of the matter but could not discuss it because it was an “intelligence issue”.

“It is too complicated to go into estimating numbers for this type of thing,” it said.